Telephone-transmitter



W. AND J. BRRELL.

TELEPHONE TRANSMITTER. APPLlcAloN FILED Auw-s. 1.917.

Patented June 1, 1920.

A TTOHIVEY UNITED STATES P'TENT ori-"1o.

WILLIAM BIRRELL AND JAMES BIRRELIL,V OF CHICAGO, ILLINOIS, ASSIGNORS TO THE AUDIBLE TELEPHONE COMPANY, OF CHICAGOQILLINOIS, A CORPORATION 0F DELA- WARE.

TELEPHONE-TRANSMITTER.

Specification of Letters Patent. Patented J 1,1110 1, 1920.

Application filed August 18, 1917. .Seral'Na 187,032.

To all whom t may concern:

Be it known that we, ViLLiAM BIRRELL and JAMES BIRRELL, citizens of the United States, and residents of Chicago, county of Cook, and State of Illinois,` whose postoilice address is 1T() Randolph street west, have invented a new and useful Improvement in Telephone-Transmitters, of which the Jfollowing is a specification. f

This invention relates to telephone transmitters of the agitation type.

One object of the invention is to provide a transmitter wherein the diaphragm is loosely housed and the carbon employed as the resistance varying medium is agitated to a degree directly responsive to the periodicity of the vibrations of the voice and resistance is thereby proportionately increased through the reduction ot points of contact between the individual particles of carbon.

Another object of the invention is to provide a transmitter having an electrode chamber mounted centrally of the diaphragm and containing electrodes both movable in unison therewith through being mounted in parallel with the diaphragm and upon substantially equal distances upon either side of the diaphragm and in balanced relation thereto, so that the amplitudes of vibration of the diaphragm will be equal on each side of the plane corresponding to its state of equilibrium.

A further object of the invention is to provide a transmitter having an electrode chamber in which exists only a minute quantity of air.

A still Jfurther object of the invention is a provision of an annular sound chamber positioned between the mouth piece and the peripheral margin of the diaphragm whereby sound-waves delivered into said mouthpiece are directed throughout the entire superficial extent of the diaphragm.

One purpose of the invention is to provide an electrode chamber wherein the characteristics of the current bearing inedium are negative as the vibration increases, thus tending to reduce the flow of current through a rapid decoherence of the said medium.

To accomplish these various objects and purposes the invention broadly stated comprises an unconfined diaphragm and an electrode chamber mounted therein, and

balanced statically without counter-weights,

said electrode chamber having disposed therein-a plurality of facing electrodes; a

negative resistance current bearing medium in the chamber and incontact with the electrodes; terminals for said electrodes, and ak casing for said diaphragm including an antelephone transmitter, and,

Fig. '2 is a rear elevation of the same with the back plate partly broken away.

Referring to said views, the reference numeral 1 indicates a casing formed with a centrally threaded aperture with which the mouth-piece is connected. The back plate 3 is secured upon the reverse side of said casing as with screws 5, inclosing a diaphragm compartment 6.

A circular diaphragm plate 7 is loosely housed within said compartment. A rubber insulating ringl 8 is engaged about the peripheral'edges of said diaphragm. The casing 1 is formed with a shoulder 9 and upon the opposite side of said diaphragm felt blocks 10 are positioned between which and said shoulder the diaphragm is maintained on its edge in unconined condition.

The diaphragm is formed with a centrally disposed cupped portion 11. A cup-member 12 of substantially similar configuration' to the portion 11 of the diaphragm is secured as by rivets 13 to the diaphragm to afford an electrode lchamber 15 whose interior form is substantially equal or symmetrical upon opposite sides of the plane ofthe diaphragm,

corresponding to its state of equilibrium.

Said electrodes are arranged with oppositely disposed plane surfaces parallel and said surfaces are likewise parallel to the main plane of the diaphragm.

Electrodes indicated generally by the numerals 16 and 17 are rigidly connected to the end 'walls of said cup-members 11 and 12 respectively. Said cup-member 12 is insulated by washer 21 from the diaphragm and the rivets 13 are also insulated from the diaphragm as indicated at 14. Circuit Wires 18 and 19 are in -electrical connection with studs 2O of the respective electrodes 16 and 17.

v direct connection with the electrode 17. y quantity of carbon granules 22 fill approxiscrew bolt 13 which conducts the electrical Y current to the cup-member 12, which is in mately two thirds of the space within the said chamber 15 when at rest.

Opposite the annular planel portion 23 of the diaphragm the casing 1 is formed with an annular depression 25 from its rearward side, affording an annular sound-wave Vexpansion-chamber 26. There is provided a relatively wide passage 27 between said chamber 26 and the moutl1-piece2 whereby sound waves entering` the mouth-piece are distributed to affect the entire superfecies of the diaphragm., The provision of said chamber 26 in the type of apparatus herein described has been demonstrated to improve the action of the diaphragm by equalizing the air resistance upon the opposite sides ofl the diaphragm in its re-actions in response. v,to the sound-waves of the voice.

Under the impact of sound-waves the diaphragm is vibrated and the granular material contained in the chamber 15 is agitated varying the resistance to the current passing between the electrodes Ain accordance with the degree of agitation.,

To increase the activity of the carbon granules and improve the responsiveness of the device we may exhaust a portion of the atmospheric air from the chamber 15.sealing all crevices extending thereinto, as by cement.

By thus exhausting the air in the electrode chamber the resistance to the movement of the carbon granules is materially decreased and as a result exceedingly slight movements of the diaphragm result in a corresponding change of resistance of the carbon granules and a change of current flows in the transmitter circuit.

One of the -principal advantages afforded by our invention is that a transmitter of the agitation type is produced in which the yeffect of inertia of the loose carbon granules is reduced to have the least possible effect. The efficiency of the present form of transmitter is largely dependent upon the responsiveness of the carbon granulesto agitation, the variation of resistance, being principally due to inter-granular change of arrangement of .the mass of carbon within the chamber 15 through the vibration of the diaphragm. The inertia of the v mass of carbon within the chamber is a form of compression and to the extent that it is present reduces the activity of the granules and defeats the effectiveness of the instrument. By positioning the electrodes parallel and balancing them upon opposite sides of the diaphragm we obtain an equalization of the force of inertia in the loose body of granules exerted upon the oppositev electrodes and thus reduce the adverse leffect to the lowest terms.

What is claimed is z- Y 1. A transmitter of the class described comprising a casing, a diaphragm in the casing, a central depression in the diaphragm, a cover securedvover the depression projecting from the plane of the diaphragm the same distance as the depression and in the opposite direction, a pair of electrodes secured between the cover and the depression at equal distances from the plane of the diaphragm, and means for sealing the cover to the depression whereby the space therebetween may be made air-tight and the air exhausted therefrom.

2. In a telephone transmitter of the class described a freely vibratable diaphragm and.

an air-tight electrode chamber at the center of the diaphragm, said chamber being balanced with respect to the plane of the diaphragm and having the air partially eX- the plane of said diaphragm, said electrode Y Y chamber being air tight and having a portion of the air exhausted therefrom.

Signed at Chicago7 Illinois, this 14th day of Aug., 1917.

WILLIAM BIRRELL. yJAMES BIRRELL. Y 

